To ensure that you understand the material in this chapter, you should review the meanings of the following bold terms in the following summary and ask yourself how they relate to the topics in the chapter.
Atoms can share pairs of valence electrons to obtain a valence shell octet. This sharing of electrons is a covalent bond. A species formed from covalently bonded atoms is a molecule and is represented by a molecular formula, which gives the number of atoms of each type in the molecule. The two electrons shared in a covalent bond are called a bonding pair of electrons. The electrons that do not participate in covalent bonds are called nonbonding pairs (or lone pairs) of electrons. A covalent bond consisting of one pair of shared electrons is called a single bond.
Covalent bonds occur between nonmetal atoms. Naming simple covalent compounds follows simple rules similar to those for ionic compounds. However, for covalent compounds, numerical prefixes are used as necessary to specify the number of atoms of each element in the compound.
In some cases, more than one pair of electrons is shared to satisfy the octet rule. Two pairs of electrons are shared by two atoms to make a double bond. Three pairs of atoms are shared to make a triple bond. Single, double, and triple covalent bonds may be represented by one, two, or three dashes, respectively, between the symbols of the atoms.
The distance between two covalently bonded atoms is the bond length. Bond lengths depend on the types of atoms participating in the bond as well as the number of electron pairs being shared. A covalent bond can be a polar covalent bond if the electron sharing between the two atoms is unequal. If the sharing is equal, the bond is a nonpolar covalent bond. Because the strength of an atom’s attraction for electrons in a bond is rated by the atom’s electronegativity, the difference in the two atoms’ electronegativities indicates how polar a covalent bond between those atoms will be.
The mass of a molecule is called its molecular mass and is the sum of the masses of the atoms in the molecule. The shape of a molecule can be predicted using valence shell electron pair repulsion (VSEPR), which uses the fact that the negative electrons in covalent bonds repel each other as much as possible. Molecules with polar bonds are polar except when the bond polarities cancel due to symmetry.
Organic chemistry is the chemistry of carbon compounds. Carbon forms covalent bonds with other carbon atoms and with the atoms of many other elements. The simplest organic compounds are hydrocarbons, which consist solely of carbon and hydrogen. Hydrocarbons containing only single bonds are called alkanes (saturated hydrocarbons). Hydrocarbons containing carbon–carbon double bonds are alkenes, while hydrocarbons with carbon–carbon triple bonds are alkynes. Carbon-carbon double and triple bonds are examples of functional groups, atoms or bonds that impart a characteristic chemical function to the molecule. Other functional groups include the alcohol functional group (OH) and the carboxyl functional group (COOH). They are the characteristic functional group in organic compounds called alcohols and carboxylic acids.